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The spatial distributions of marine fish populations are influenced by environmental conditions, intrinsic properties of the populations, and prior distribution. The influence of these factors may not be consistent across age classes. For this study, age composition estimates for walleye pollock (Gadus chalcogrammus) collected on bottom-trawl surveys in the Bering Sea were used to estimate range correlation indices, population centers of gravity, and effective area occupied. Age- specific density maps suggested a circular ontogenic migration during the summer feeding season, with the youngest and oldest groups most broadly distributed. Range correlation analysis among age groups and year classes provided clear evidence of a population cohort effect in the spatial distribution of the population. Variance decomposition analysis indicated that the variance in the spatial distribution of age groups during summer was influenced by the initial distribution of that cohort as recruits. Model-based analyses showed that extrinsic temperature variables affected the youngest and oldest age classes the most, but provided no indication of age-related effects for intrinsic population factors. This study showed that both cohort and age-specific factors are important drivers of spatial distribution. Key words: demographics, age composition, distribution, walleye pollock, modeling, VAST La repartition spatiale de populations de poissons marins est influencee par les conditions ambiantes, des proprietes intrinseques des populations et la repartition prealable. L'influence de ces facteurs pourrait ne pas etre uniforme d'une classe d'age a l'autre. Nous avons utilise des estimations de la composition par age pour des goberges de l'Alaska (Gadus chalcogrammus) prelevees dans le cadre d'evaluations au chalut de fond dans la mer de Behring pour estimer des indices de correlation des aires de repartition, les centres de gravite de la population et la superficie occupee effective. Des cartes de densite selon l'age indiqueraient une migration ontogenetique circulaire durant la saison d'alimentation estivale, les groupes les plus jeunes et les plus vieux presentant les repartitions les plus vastes. L'analyse de correlation des aires de repartition de differents groupes d'age et classes d'annee fournit des preuves claires d'un effet populationnel de la cohorte dans la repartition spatiale de la population. L'analyse de decomposition de la variance indique que la variance de la repartition spatiale des groupes d'age durant l'ete est influencee par la repartition initiale de la cohorte au moment du recrutement. Des analyses reposant sur des modeles montrent que des variables extrinseques associees a la temperature exercent la plus grande influence sur les classes d'age les plus jeunes et les plus vieilles, mais elles ne revelent aucun effet relie a l'age de facteurs intrinseques a la population. L'etude demontre que des facteurs associes tant a la cohorte qu'a l'age exercent une importante influence sur la repartition spatiale. [Traduit par la Redaction] Mots-cles : demographie, composition par age, repartition, goberge de l'Alaska, modelisation, VAST, Introduction The spatial distributions of fish populations are influenced by many factors. Environmental variables that define habitat suitability are clearly important. For example, physiological tolerances and resource availability directly affect [...]

Abstract--From late 2014 through 2017, fishery observers in the North Pacific Observer Program, National Marine Fisheries Service, were trained in the identification and sampling of skate egg cases to investigate [...]

Abstract--We analyzed skate catch data collected by observers in the North Pacific Groundfish Observer Program (NPGOP) from 1998 through 2008 to document recent changes in the identification of skates by [...]

Skates are a diverse group of dorso-ventrally compressed cartilaginous fish found primarily in high-latitude seas. These slow-growing oviparous fish deposit their fertilized eggs into cases, which then rest on the seafloor. Developing skates remain in their cases for 1–4 years after they are deposited, meaning the abiotic characteristics of the deposition sites, such as current and substrate type, must interact with the capsule in a way to promote long residency. Egg cases are morphologically variable and can be identified to species. Both the gross morphology and the microstructures of the egg case interact with substrate to determine how well a case stays in place on a current-swept seafloor. Our study investigated the egg case hydrodynamics of eight North Pacific skate species to understand how their morphology affects their ability to stay in place. We used a flume to measure maximum current velocity, or "break-away velocity," each egg case could withstand before being swept off the substrate and a tilt table to measure the coefficient of static friction between each case and the substrate. We also used the programing software R to calculate theoretical drag on the egg cases of each species. For all flume trials, we found the morphology of egg cases and their orientation to flow to be significantly correlated with break-away velocity. In certain species, the morphology of the egg case was correlated with flow rate required to dislodge a case from the substrate in addition to the drag experienced in both the theoretical and flume experiments. These results effectively measure how well the egg cases of different species remain stationary in a similar habitat. Parsing out attachment biases and discrepancies in flow regimes of egg cases allows us to identify where we are likely to find other elusive species nursery sites. These results will aid predictive models for locating new nursery habitats and protective policies for avoiding the destruction of these nursery sites. [ABSTRACT FROM AUTHOR]

Abstract--Six years of bottom-trawl survey data, including over 6000 trawls covering over 200 [km.sup.2] of bottom area throughout Alaska's subarctic marine waters, were analyzed for patterns in species richness, diversity, [...]

The population structure and demographic history of a pelagic lumpsucker, Aptocyclus ventricosus, were investigated on the basis of sequence variation in the mitochondrial cytochrome b gene (1038 bp). The haplotype network clearly recovered two haplotype groups, consisting of western and eastern North Pacific individuals, except for some specimens collected from offshore of Tohoku, northern Japan. The geographic distribution of haplotypes suggests that the ocean currents in the North Pacific have shaped the population structure of the species after historical vicariant events between the Kuril Islands and Kamchatka Peninsula. In addition, the demographic histories of the two haplotype groups were quite different, suggesting that the western North Pacific group experienced a population expansion starting around 10,000 years ago, while the population size of the eastern North Pacific group has remained more stable. [ABSTRACT FROM AUTHOR]

Poleward species range shifts have been predicted to result from climate change, and many observations have confirmed such movement. Poleward shifts may represent a homogeneous shift in distribution, seasonal northward movement of specific populations, or colonization processes at the poleward edge of the distribution. The ecosystem of the Bering Sea has been changing along with the climate, moving from an arctic to a subarctic system. Several fish species have been observed farther north than previously reported and in increasing abundances. We examined one of these fish species, Pacific cod, in the northern Bering Sea (NBS) to assess whether they migrated from another stock in the eastern Bering Sea (EBS), Gulf of Alaska, or Aleutian Islands, or whether they represent a separate population. Genetic analyses using 3,599 single nucleotide polymorphism markers indicated that nonspawning cod collected in August 2017 in the NBS were similar to spawning stocks of cod in the EBS. This result suggests escalating northward movement of the large EBS stock during summer months. Whether the cod observed in the NBS migrate south during winter to spawn or remain in the NBS as a sink population is unknown. [ABSTRACT FROM AUTHOR]

The zoarcoid family Bathymasteridae contains seven species in three genera (Bathymaster, Rathbunella, Ronquilus) found in the North Pacific Ocean. Although several synapomorphies have been identified for the family, molecular analyses recover the family as a paraphyletic grade. The goals of this study are to provide a description of the skeleton of R. jordani as a baseline contribution for future systematic comparisons among all bathymasterid taxa and zoarcoids. We used our osteological study to discuss ontogenetically variable characters that appear to carry phylogenetic signal within Zoarcoidei. Finally, we discuss the systematic relationships of Bathymasteridae, including its monophyly and their systematic relationships. The vertebrae of Bathymasteridae develop in two distinct patterns. In Ronquilus and Bathymaster, the vertebrae initially form in the mid‐caudal region and development proceeds both anteriorly and posteriorly until the entire vertebral column is complete. In contrast, in Rathbunella the vertebrae initially form immediately posterior to the skull and development proceeds posteriorly; this is interpreted to be plesiomorphic. Other characters that were clarified (e.g., presence of well‐developed teeth on the gill rakers of Ronquilus) or described (e.g., variation in fusion caudal skeleton elements across Zoarcoidei) now must be evaluated in a taxonomically comprehensive systematic analysis of Zoarcoidei. [ABSTRACT FROM AUTHOR]

Species composition data collected by observers in the North Pacific Observer Program are critical to the effective management of Alaska’s commercial fisheries. However, there has been no attempt to quantify the reliability of observer species identifications. Digital cameras were issued to over 120 groundfish observers, who were instructed to document via digital photographs a pre-selected series of fish identifications and submit the photos for analysis at the end of their deployments. Identifications represented by the photos were then assessed visually by the author for identification accuracy. Over 3000 individual identifications were documented, and over 99% of those identifications were correct. Identification accuracy rates for each of the commercial species groups identified by observers (flatfishes, cods, rockfishes, and salmon) were over 98%. Accuracy rates for some non-target species groups, such as sculpins and smelts, were slightly lower. Identifications documented for this study represent a broad spectrum of target fisheries, gear types, and observer experience levels, and therefore are likely to be a reasonable representation of observer identification accuracy throughout the Observer Program. Although there are potential sources of bias that may have inflated these accuracy rates, this study suggests that the overall reliability of species identifications in the North Pacific Observer Program is quite high. [ABSTRACT FROM AUTHOR]